1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having an electronic timer being free from a battery.
2. Description of the Related Art
In recent years, an electronic timer being free from a battery, i.e., an aging device the output of which changes with elapsed time begins to be considered to be used in fields of contents distribution, credit cards, rental digital products, rental digital software, and the like.
The aging device has a stack gate structure constituted by a floating gate and a control gate electrode and functions as an electronic timer which measures a predetermined period by a retention (aging) of electric charges in the floating gate (for example, see JP-A 2004-172404 (KOKAI) and JP-A 2005-310824 (KOKAI)).
According to the aging device, for example, a tunnel insulating film is changed in thickness to make it possible to change the aging.
However, electric charge leakage from the floating gate changes depending on a manufacturing fluctuation. For this reason, in order to cause the aging device to function as an accurate electronic timer, a complex circuit to eliminate an error generated by the manufacturing fluctuation is required.
As fields in which the aging devices are used spread, the agings of the aging devices must be set to cope with business models, respectively. Since this means that a plurality of production lines of aging devices must be installed in correspondence with the agings, the production cost increases.